This invention relates to a fiber-based composite material, to a process for the production of fiber-based composite materials and to the use of these materials for the production of consumer articles.
Fiber composites consist at least of fibers and a matrix material. The function of the fibers is to strengthen the material. More particularly, the fibers absorb tensile forces acting on the material while the matrix fills voids between the fibers and coats the fibers. The matrix thus transmits the shear forces acting on the composite material. In addition, the matrix protects the coated fibers from outside influences such as, for example, the penetration of water or moisture, oxidative or photo-oxidative influences. Known fiber composites include, for example, glass-fiber-, metal-fiber- or carbon-fiber-reinforced plastics. By virtue of their high strength, durability and reproducibility, composites such as these have hitherto been successfully used in many fields. However, in view of the need for sustainable development, products based on biomass and/or agricultural products as renewable raw materials have also been increasingly in demand for composite materials. In contrast to petrochemical and fossil raw materials, renewable raw materials are never exhausted and, through the cultivation of new plants, can be regenerated at any time by photosynthesis.
Plastics reinforced by natural fibers are known per se. Their advantages over glass-fiber-reinforced plastics in regard to raw material base, ecobalance, safety at work, weight and thermal disposal have already been described, cf. for example Kohler, R.; Wedler, M.; Kessler, R.: xe2x80x9cNutzen wir das Potential der Naturfasern?xe2x80x9d in: Gxc3xclzower Fachgesprxc3xa4che xe2x80x9cNaturfaserverstxc3xa4rkte Kunststoffexe2x80x9d (Ed. Fachagentur Nachwachsende Rohstoffe, Gxc3xclzow 1995), pages 95-100, and xe2x80x9cLeitfaden Nachwachsende Rohstoffe, Anbau, Verarbeitung, Produktexe2x80x9d, 1st Edition, Heidelberg: Mxc3xcller, 1998, more particularly Chapter 8. The matrixes used may be divided into thermoplastic and thermoset systems. Systems with thermoplastic matrixes based on renewable raw materials are known. Thus, EP-A-687 711 describes a fibre composite of biodegradable fibers and a matrix of biodegradable material. Cellulose acetate, lignin, starch and starch derivatives are proposed as suitable thermoplastic materials for the matrix. Products such as these have been found to be unsatisfactory in regard to processability, mechanical properties in important applications and price.
DE-A-196 47 671 describes a fiber composite with a fibrous material for reinforcement and a matrix material based on shellac. The matrix material may contain a crosslinking agent. The main disadvantage of this thermoset matrix material is the very limited availability of shellac.
Other thermoset systems available at the present time are mainly polymer systems of which the raw materials are very largely petrochemical in origin (polyurethanes, epoxy resins, polyesters, etc.). In the field of polyurethanes, some proposals have been put forward with a view to developing native-based raw materials. For example, EP-A-634 433 proposes reaction products of a polyester obtainable by self-condensation of ricinoleic acid with an aromatic polyisocyanate as binders for the production of composite materials.
In addition, DE-A41 19 295 proposes an ecofriendly composite material of natural fibers and plastics of the polyurethane-polyester and/or polyurethane-polyamide type which contain hydroxyfunctional natural fatty acids of unchanged length or derivatives thereof.
In xe2x80x9cAngewandte makromolekulare Chemiexe2x80x9d 249 (1997), pages 79 to 92, R. Mxc3xclhaupt, D. Hoffmann, S. Lawson and H. Warth describe flexible, semiflexible and rigid polyester networks based on maleinized oils of vegetable oils, such as soybean, rapeseed and linseed oil, as anhydride-functional hardeners with epoxy resins based on bisphenol A/diglycidyl ether or epoxidized vegetable oils. They also describe unsaturated polyester resins based on maleic anhydride, epoxidized vegetable oils and styrene which may optionally be reinforced with natural short fibers, such as flax or hemp. The processability of such resins by existing processing machines is not discussed.
Factors of paramount importance in the development of composite materials besides the choice of ecologically safe renewable raw materials are, of course, the mechanical properties of those materials including, in particular, high tensile strength.
The problem addressed by the present invention was to provide composite materials in which both the reinforcing materials and the matrix materials would be largely based on renewable raw materials and which would have improved mechanical properties in relation to known materials.
It has surprisingly been found that, with materials based on renewable raw materials, it is possible by limiting the quantities of fibers used, based on the matrix material, to obtain materials which have advantageous mechanical properties.